Apparatus and Method for Fast Phase Locked Loop (PLL) Settling for Cellular Time-Division Duplex (TDD) Communications Systems

ABSTRACT

A communications device is disclosed that adjusts a target signal to allow a reference phase locked loop (PLL) to lock onto a reference signal that is related to a desired operating frequency in a first mode of operation. The reference PLL locks onto the reference signal when the target signal is calibrated to be proportional to the reference signal. As the communications device transitions between the first mode of operation and a second mode of operation, the communications device performs a shorten calibration cycle on the reference PLL. The reference phase locked loop (PLL) locks onto the reference signal in response to the shorten calibration cycle in the second mode of operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentAppl. No. 61/556,094, filed Nov. 4, 2011, which is incorporated hereinby reference in its entirety.

BACKGROUND

1. Field of Disclosure

The present disclosure relates generally to a phase locked loop (PLL)and specifically to calibration of a voltage controlled oscillator (VCO)for the cellular phone.

2. Related Art

Cellular phones have evolved from large devices that were only capableof analog voice communications to comparatively smaller devices that arecapable of digital voice communications and digital data communications,such as Short Message Service (SMS) for text messaging, email, packetswitching for access to the Internet, gaming, Bluetooth, and MultimediaMessaging Service (MMS) to provide some examples. In addition to thesecapabilities, the cellular phones of today have additionalnon-communication related capabilities, such as a camera with videorecording, an MPEG-1 Audio Layer 3 (MP3) player, and softwareapplications such as a calendar and a phone book, to provide someexamples. Even in light of these capabilities, manufacturers of cellularphones are placing even more capabilities into cellular phones andmaking these more powerful cellular phones smaller.

At the heart of each cellular phone lies a phase locked-loop (PLL). ThePLL is responsible for providing an appropriate transmit frequency forthe cellular phone prior to commencement of a transmit mode ofoperation. The PLL is also responsible for providing an appropriatereceive frequency for the cellular phone prior to commencement of areceive mode of operation. In order to properly provide the appropriatetransmit and/or receive frequency for the cellular phone, a voltagecontrolled oscillator (VCO) located within the PLL is calibrated to theappropriate transmit and/or receive frequency of the cellular phone.Once the VCO is initially calibrated to be sufficiently proportional toa frequency and/or a phase of a reference frequency, the PLL locks thefrequency of the VCO to be proportional to the frequency and/or thephase of the reference frequency to provide the appropriate transmitand/or receive frequency. Often, additional calibration of the VCOfollowing the initial calibration is often required to ensure that theVCO is sufficiently proportional to the frequency and/or the phase ofthe reference frequency to the appropriate transmit and/or receivefrequency. For example, an additional calibration may be required oncethe cellular phone transitions from the transmit mode of operation tothe receive mode of operation and/or from the receive mode of operationto the transmit mode of operation.

Communications standards provide a certain time window for an initialcalibration of the VCO. However, in certain communications standardsoften do not provide sufficient time for the additional calibration,which is typically necessary when the cellular phone transitions fromthe transmit mode of operation to the receive mode of operation and/orfrom the receive mode of operation to the transmit mode of operation. Asa result, the cellular phone may not be aligned to the appropriatereceive frequency when the cellular phone switches from the transmitmode of operation to the receive mode of operation, for example.

Thus, there is a need to calibrate the VCO following the initialcalibration when transitioning from the transmit mode of operation tothe receive mode of operation and/or from the receive mode of operationto the transmit mode of operation to the appropriate transmit and/orreceive frequency of the cellular phone but to do so within the timeallotted in the respective communications standard. Further aspects andadvantages of the present disclosure will become apparent from thedetailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

Embodiments of the present disclosure are described with reference tothe accompanying drawings. In the drawings, like reference numbersindicate identical or functionally similar elements. Additionally, theleft most digit(s) of a reference number identifies the drawing in whichthe reference number first appears.

FIG. 1 illustrates a block diagram of a communications device accordingto an exemplary embodiment of the present disclosure;

FIG. 2 is a block diagram of a reference PLL that may be used in thecommunications device according to an exemplary embodiment of thepresent disclosure;

FIG. 3 is a table that represents each type of calibration that may beused by the communications device based on the communications standardand the operation to be performed by the communications device;

FIG. 4 illustrates a block diagram of a VCO according to an exemplaryembodiment of the present disclosure; and

FIG. 5 is a flowchart of exemplary operational steps of thecommunications device according to an exemplary embodiment of thepresent disclosure.

The present disclosure will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers generallyindicate identical, functionally similar, and/or structurally similarelements. The drawing in which an element first appears is indicated bythe leftmost digit(s) in the reference number.

DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE

Embodiments of this disclosure include three calibration types in whicha communications device may calibrate a phase locked loop (PLL). Thethree calibration types include a full calibration, a fine calibration,and an offset calibration. The full calibration is to be used by thecommunications device during a first engagement and/or any subsequentengagement of a communication channel by the communications device. Thefine calibration is to be used by the communications device when thereis short but sufficient time provided for the communications device totransition between modes of operation. Typically, the time provided forthe communications device is determined by the communications standard.The fine calibration includes a scaled down version of the fullcalibration and optionally applying a pre-determined offset tocompensate for the transitioning between the modes of operation. Theoffset calibration is to be used by the communications device whenlimited time is provided for the communications device to transitionbetween the modes of operation. The offset calibration includes applyinga pre-determined offset to compensate for the transitioning between themodes of operation.

The following Detailed Description refers to accompanying drawings toillustrate exemplary embodiments consistent with the present disclosure.References in the Detailed Description to “one exemplary embodiment,”“an exemplary embodiment,” “an example exemplary embodiment,” etc.,indicate that the exemplary embodiment described may include aparticular feature, structure, or characteristic, but every exemplaryembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same exemplary embodiment. Further, when a particularfeature, structure, or characteristic is described in connection with anexemplary embodiment, it is within the knowledge of those skilled in therelevant art(s) to effect such feature, structure, or characteristic inconnection with other exemplary embodiments whether or not explicitlydescribed.

The exemplary embodiments described herein are provided for illustrativepurposes, and are not limiting. Other exemplary embodiments arepossible, and modifications may be made to the exemplary embodimentswithin the spirit and scope of the present disclosure. Therefore, theDetailed Description is not meant to limit the present disclosure.Rather, the scope of the present disclosure is defined only inaccordance with the following claims and their equivalents.

Embodiments of the present disclosure may be implemented in hardware,firmware, software, or any combination thereof. Embodiments of thepresent disclosure may also be implemented as instructions stored on amachine-readable medium, which may be read and executed by one or moreprocessors. A machine-readable medium may include any mechanism forstoring or transmitting information in a form readable by a machine(e.g., a computing device). For example, a machine-readable medium mayinclude read only memory (ROM); random access memory (RAM); magneticdisk storage media; optical storage media; flash memory devices;electrical, optical, acoustical or other forms of propagated signals(e.g., carrier waves, infrared signals, digital signals, etc.), andothers. Further, firmware, software, routines, instructions may bedescribed herein as performing certain actions. However, it should beappreciated that such descriptions are merely for convenience and thatsuch actions in fact result from computing devices, processors,controllers, or other devices executing the firmware, software,routines, instructions, etc.

The following Detailed Description of the exemplary embodiments will sofully reveal the general nature of the present disclosure that otherscan, by applying knowledge of those skilled in relevant art(s), readilymodify and/or adapt for various applications such exemplary embodiments,without undue experimentation, without departing from the spirit andscope of the present disclosure. Therefore, such adaptations andmodifications are intended to be within the meaning and plurality ofequivalents of the exemplary embodiments based upon the teaching andguidance presented herein. It is to be understood that the phraseologyor terminology herein is for the purpose of description and not oflimitation, such that the terminology or phraseology of the presentspecification is to be interpreted by those skilled in relevant art(s)in light of the teachings herein.

An Exemplary Communications Device

FIG. 1 illustrates a block diagram of a communications device accordingto an exemplary embodiment of the present disclosure. A communicationsdevice 100 calibrates a reference phase lock loop (PLL) 108 to provide atarget signal 156 that is sufficiently proportional to a referencesignal 154. In this situation, the reference PLL 108 is characterized asbeing in a locked condition whereby the target signal 156 essentiallytracks the reference signal 154. For example, the target signal 156essentially tracks a phase of the reference signal 154 in the lockedcondition. However, if the target signal 156 is not sufficientlyproportional to the reference signal 154, the target signal 156 does nottrack the reference signal 154. In this situation, the reference PLL 108is characterized as being in an unlocked condition.

The communications device 100 uses the target signal 156 as a referencesignal for a receiver 118 in a receive mode of operation and as areference signal for a transmitter 116 in a transmit mode of operation.In the receive mode of operation, the receiver 118 is used as a means toreceive communications signals from a communications channel. While thetransmitter 116 is used as a means to transmit communications signalsonto the communications channel in the transmit mode of operation.

The communications device 100 calibrates the reference PLL 108 in eitherthe receive mode of operation or the transmit mode of operation. As tobe further discussed below, the communications device 100 adjusts thecalibration of the reference PLL 108 to cause the reference PLL 108enter into the locked condition after switching from the receive mode ofoperation to the transmit mode of operation and/or from the transmitmode of operation to the receive mode of operation. The communicationsdevice 100 adjusts the calibration of the target signal 156 within thetime allowed by a communications standard such as Second-GenerationWireless Telephone Technology (2G), Third-Generation Wireless TelephoneTechnology (3G), Long Term Evolution Frequency-Division Duplexing (LTEMD), Long Term Evolution Time-Division Duplexing (LTE TDD), and TimeDivision Synchronous Code Division Multiple Access (TD-SCDMA) and/or anyother suitable communications standard that will be apparent to thoseskilled in the relevant art(s) without departing from the spirit andscope of the present disclosure.

As shown in FIG. 1, the communications device 100 includes a referenceoscillator 102, the reference PLL 108, a switching module 110, thetransmitter 116, the receiver 118, and a controller module 120. Thereference oscillator 102 provides the reference signal 154 to thereference PLL 108. The reference signal 154 is related to a desiredoperating frequency of the communications device 100. For example, afrequency of the reference signal 154 may be approximately equal or aninteger or fractional multiple of the desired operating frequency of thecommunications device 100. The reference oscillator 102 includes anoscillator 104 and an optional scaling module 106. The oscillator 104provides a reference signal 150. The optional scaling module 106multiplies and/or divides the reference signal 150 to generate thereference signal 154.

As discussed above, the reference PLL 108 provides the target signal 156that essentially tracks the reference signal 154 in the lockedcondition. For example, the reference PLL 108 causes a frequency and/ora phase of the target signal 156 to be approximately equal to afrequency and/or a phase of the target signal 156. As another example,the reference PLL 108 causes the phase of the target signal 156 to beapproximately equal to the phase of the target signal 156 and thefrequency of the target signal 156 to be proportional to, namely aninteger or fractional multiple of, the frequency of the target signal156.

The switching module 110 may provide the target signal 156 as a transmitreference signal 162 to the transmitter 116 in the transmit mode ofoperation or as a receive reference signal 164 to the receiver 118 inthe receive mode of operation. The reference PLL 108 provides asynthesized transmit signal 162 to the transmitter 116 that may be usedto upconvert, to modulate, and/or to encode signals for transmissiononto the communications channel. Similarly, the reference PLL 108provides a synthesized receive signal 164 to the receiver 118 that maybe used to downconvert, to demodulate, and/or to decode signals that arereceived from the communications channel.

The controller module 120 calibrates the reference PLL 108 as thecommunications device 100 engages the communications channel in a firstmode of operation, such as the receive mode of operation to provide anexample, and calibrates the reference PLL 108 as the communicationsdevice 100 switches from the first mode of operation to a second mode ofoperation, such as the transmit mode of operation. The controller module120 monitors an appropriate tuning signal 168 of the reference PLL 108which is indicative of a difference between the reference signal 154 andthe target signal 156. The controller module 120 adjusts the controlsignal 166 during various calibrations, that are to be discussed below.

The controller module 120 initially calibrates the reference PLL 108 toprovide the target signal 156 that is proportional to the frequencyand/or the phase of the reference signal 154 when the communicationsdevice 100 engages the communications channel. During this initial orfull calibration, the controller module 120 executes an extensivecalibration cycle to calibrate the reference PLL 108 such that it locksonto the reference signal 154. Typically, this full calibration involvesaligning the frequency and/or the phase of the target signal 156 to besufficiently proportional to the frequency and/or the phase of thereference signal 154 such that the reference PLL 108 may lock onto thereference signal 154. The full calibration of the reference PLL 108 mayconsume a large quantity of time in order to properly calibrate thetarget signal 156. For example, the TD-SCDMA communications standardallows at most 120 microseconds to perform the full calibration when thecommunications device 100 engages the communications channel.

Typically, the controller module 120 performs the full calibration whilethe communications device 100 is operating in the first mode ofoperation, such as the receive mode of operation to provide an example.However, those skilled in the relevant art(s) will recognize that thecontroller module 120 may also perform the full calibration while thecommunications device 100 is operating in the transmit mode of operationwithout departing from the spirit and scope of the present disclosure.Following the initial engagement of the communications device 100 to thecommunications channel in the first mode of operation, thecommunications device 100 may transition from the first mode ofoperation to the second mode of operation, such as the transmit mode ofoperation to provide an example. Ideally, loading of the reference PLL108 by the receiver 118 in the receive mode of operation issubstantially similar to loading of the reference PLL 108 by thetransmitter 116 in the transmit mode of operation. However, in practice,an input impedance of the transmitter synthesizer 116 differs from aninput impedance of the receiver 118. This difference between the inputimpedances of the transmitter 116 and the receiver 118 may cause thereference PLL 108 to enter into the unlocked condition as thecommunications device 100 transitions from the first mode of operationto the second mode of operation. In the unlocked condition, the targetsignal 156 does not track the reference signal 154 unless the controllermodule 120 performs another calibration of the reference PLL 108 tocause the reference PLL 108 to once again lock onto the reference signal154.

However, the controller module 120 may no longer have sufficient time toperform another full calibration of the reference PLL 108 whentransitioning from the first mode of operation to the second mode ofoperation. The amount of time the communications device 100 may take inperforming this transition is typically specified by variouscommunications standards. The controller module 120 must perform thisother calibration of the reference PLL 108 within these specified timeswhich typically are significantly less than time required to perform thefull calibration. For example, the TD-SCDMA communications standardrequires the communications device 100 to transition from the transmitmode of operation to the receive mode of operation in approximately 12.5microseconds; therefore, any calibration of the reference PLL 108following a transition from the transmit mode of operation to thereceive mode of operation must be done in 12.5 microseconds as comparedto 120 microseconds allowed for the full calibration. Thus, a shortenedcalibration is required for the reference PLL 108 when transitioningfrom the first mode of operation to the second mode of operation.

The controller module 120 may perform the shortened calibration whentransitioning from the first mode of operation to the second mode ofoperation. The shortened calibration allows for a quick adjustment ofthe target signal 156 while leaving sufficient time for the rreferencePLL 108 to settle to the locked condition. Some of the communicationsstandards provide for a longer duration of time to transition from thefirst mode of operation to the second mode of operation when compared toother communications standards. For example, the TD-SCDMA communicationsstandard allows 12.5 microseconds to calibrate when transitioning fromthe transmit mode of operation to the receive mode of operation and theLTE TDD communications standard allows 47 microseconds to calibrate whentransitioning between these modes of operations.

The controller module 120 may perform a fine calibration for thosecommunications standard that specify longer durations of time totransition from the first mode of operation to the second mode ofoperation and an offset calibration for those communications standardthat specify shorter durations of time to transition from the first modeof operation to the second mode of operation. The controller module 120performs the offset calibration by adjusting the control signal 166 by apredetermined amount. In an exemplary embodiment, the predeterminedamount represents a pre-known shifting of the control signal 166 thatresults from transitioning between the first mode of operation and thesecond mode of operation. The pre-known shifting of the control signal166 may be determined from an initial product evaluation of thecommunications device 100 to determine the shift of the control signal166 as the communications device transitions.

For example, the controller module 120 calibrates the reference PLL 108to provide the target frequency 156 at a first frequency in the receivemode of operation during the full calibration. In this example, thetarget frequency 156 shifts to a second frequency when thecommunications device 100 transitions from the first mode of operationto a second mode of operation. In this example, the controller module120 performs the offset calibration to adjust the target frequency 156from the second frequency to the first frequency. After adjusting thetarget signal 156 by a predetermined amount, the reference PLL 108settles to the locked condition within the duration of time specified bythe communications standards.

The fine calibration includes the offset calibration, as discussedabove, as well as another adjustment of the target frequency 156 tocompensate for operational conditions, such as temperature to provide anexample, of the communications device 100. Typically, this otheradjustment takes sufficiently less time to perform than the fullcalibration. After adjusting the target signal 156 using the finecalibration, the reference PLL 108 settles to the locked conditionwithin the duration of time specified by the communications standards.

Typically, the offset calibration is less precise than both the fullcalibration and the fine calibration but requires less time to completethan both the full calibration and the fine calibration. For example,the TD-SCDMA communications standard allows 75 microseconds to calibratewhen switching from the receive mode of operation to the transmit modeof operation. The fine calibration may be completed within the 75microseconds allowed. As a result, the controller module 120 may selectthe fine calibration over the offset calibration because the 75microseconds may be sufficient to complete the fine calibration whileproviding a more precise calibration than the offset calibration. Asanother example, the TD-SCDMA communications standard limits the time tocalibrate when switching from the transmit mode of operation to thereceive mode of operation to 12.5 microseconds. The fine calibration maynot be completed within the 12.5 microseconds allowed but the offsetcalibration may be completed within the 12.5 microseconds. As a result,the controller module 120 may select the offset calibration over thefine calibration.

An Exemplary Reference PLL

FIG. 2 is a block diagram of a reference PLL that may be used in thecommunications device according to an exemplary embodiment of thepresent disclosure. A reference PLL 200 represents a closed-loopfeedback control system that generates the target signal 156 in relationto a frequency and a phase of the reference signal 154. In other words,the reference PLL 200 performs frequency multiplication and/or division,via a negative feedback mechanism, to generate the target signal 156 interms of the reference signal 154. The reference PLL 200 may beimplemented using a phase/frequency detector (PFD) 202, a charge pump204, a loop filter 206, a voltage controlled oscillator (VCO) 208, anoptional integer frequency divider 210, an optional dithering module212, and a controller 214. The reference PLL 200 may represent anexemplary embodiment of the reference PLL 108.

The PFD 202 converts a difference between the frequency and/or the phaseof the reference signal 154 and a phase and/or a frequency of a dividedfeedback signal 258 into an error signal 250. Specifically, the PFD 202produces the error signal 250 by comparing the frequency and/or thephase of the divided feedback signal 258 and the frequency and/or thephase of the reference signal 154 to detect for deviations between thereference signal 154 and the divided feedback signal 258. When the phaseand the frequency of the error signal 250 and the phase and thefrequency of the divided feedback signal 258 are substantiallyequivalent, the reference PLL 200 is in the locked condition. In thelocked condition, the error signal 250 is proportional to the phasedifference between the reference signal 154 and the divided feedbacksignal 258.

The charge pump 204 converts the error signal 250 to a voltage/currentdomain representation, denoted as a charge pump output 252, to controlthe frequency of the VCO 208. When the reference PLL 200 is the unlockedcondition, the charge pump 204 increases or decreases the charge pumpoutput 252 based on the error signal 250. When the reference PLL 200 isin the locked condition the error signal 250 is minimized and the chargepump 204 maintains the charge pump output 252 at a substantially fixedvalue.

The loop filter 206 may be used to remove undesirable noise from thecharge pump output 252 to generate a tuning signal 254. The loop filter206 may be implemented as a low pass filter to suppress high frequencycomponents in the charge pump output 252 to allow a direct current (DC),or near DC, component of the charge pump output 252 to control the VCO208. The loop filter 206 also maintains stability of the reference PLL200.

The VCO 208 is a voltage to frequency converter. Specifically, the VCO208 produces the target signal 156 based upon the tuning signal 254 andthe frequency control signal 268. Typically, the controller 214 adjuststhe frequency control signal 268 until the target signal 156 issufficiently related to the reference signal 154 during the fullcalibration. For example, the controller 214 may cycle through differentcombinations of the frequency control signal 268 using a searchingalgorithm, such as a binary search tree algorithm, a recursionalgorithm, a Stern-Brocot algorithm and/or any other suitable searchthat will be apparent to those skilled in the relevant art(s) withoutdeparting from the spirit and scope of the present disclosure until thetarget signal 156 is sufficiently related to the reference signal 154.The tuning signal 254 is used to further adjust the target signal 156until it is approximately equal or an integer or fractional multiple ofthe reference signal 154. In an exemplary embodiment, the frequencycontrol signal 268 used to coarsely steer the target signal 156 to besufficiently related to the reference signal 154 to allow the VCO 208 tolock onto the reference signal 154 by finely steering the target signal156 using the tuning signal 254.

The optional integer frequency divider 210 is located in a feedback pathof the reference PLL 200. The optional integer frequency divider 210divides the target signal 156 by an integer N to provide the dividedfeedback signal 258. The optional integer frequency divider 210 mayadjust the integer N in response to a channel transmission signal 262.

The optional dithering module 212 allows the reference PLL 200 to ditherthe divide value over time between two or more integer values to obtainan effective time averaged fractional division factor. Morespecifically, the optional dithering module 212 selects between the twoor more integer values for each iteration of the reference PLL 200 inresponse to a division code 260, so that on average, a fractionaldivision factor can be represented. The optional dithering module 212generates the division code 260 in response to the divide ratio controlsignal 262.

The controller module 214 calibrates the reference PLL 200 in one of thefull calibration, the fine calibration, and/or the offset calibration.The controller module 214 illustrates an exemplary implementation of thefull calibration, the fine calibration, and/or the offset calibrationthat were discussed above. The controller module 214 initiallycalibrates the reference PLL 200 to provide the target signal 156 thatis proportional to the frequency and/or the phase of the referencesignal 154 when a communications device, such as the communicationsdevice 100 to provide an example, engages a communications channel.

The controller module 214 may provide the channel transmission signal262 that causes the optional dithering module 212 to provide the divideratio control signal 262 that corresponds to the communications channel.The controller module 214 provides a first value for the frequencycontrol signal 268 to cause the VCO 208 to provide the target signal 156at a first frequency. The controller module 214 monitors the tuningsignal 254 once the target signal 156 has reached the first frequency.The controller module 214 compares the tuning signal 254 to apredetermined tuning signal to determine whether the reference PLL 200is in the locked condition. The predetermined tuning signal represents apre-known tuning signal that is presented within the reference PLL 200when the reference PLL 200 is the locked condition. For example, thepre-known tuning signal may represent a DC voltage when the referencePLL 200 is the locked condition. The controller module 214 compares amagnitude of a difference between the tuning signal 254 and thepre-known tuning signal to a locking threshold. When magnitude of thedifference is less than or equal to the locking threshold, the targetsignal 156 is sufficiently related to the reference signal 154. In thissituation, the reference PLL 200 enters in the locked condition to trackthe reference signal 154.

However, when the magnitude of the difference is greater than thelocking threshold, the target signal 156 is not sufficiently related tothe reference signal 154. In this situation, the reference PLL 200 is inthe unlocked condition. The controller module 214 then provides a secondvalue for the frequency control signal 268 to cause the VCO 208 toprovide the target signal 156 at a second frequency. The controllermodule 214 determines whether the second frequency causes the referencePLL 200 to enter into the locked condition. If not, the controllermodule 214 continues to adjust the frequency control signal 268 untilthe VCO 208 enters into the locked condition. However, this example isnot limiting, those skilled in the relevant art(s) will recognize thatother methods may be used in tuning the reference PLL 200 so that thereference PLL 200 enters into the locked condition.

After receiving communications signals from the communications channelin the receive mode of operation, the communications device maytransition from the receive mode of operation to the transmit mode ofoperation. After transmitting communications signal onto thecommunications channel, the communications device may transition fromthe transmit mode of operation back to the receive mode of operation orengage another communications channel. As discussed above, thecontroller module 214 may calibrate the reference PLL 200 using the finecalibration, and/or the offset calibration while the communicationsdevice is transitioning between these modes of operation. Typically,selection of the fine calibration and or the offset calibration is basedon the communications standard in which the communications device isoperating.

For example, as shown in FIG. 3, the communications device may beoperating in the LTE TDD standard. When the communications devicetransitions from the receive mode of operation to the transmit mode ofoperation, the LTE TDD standard allows 71.3 microseconds for thecontroller module 214 to calibrate the VCO 208 so that the reference PLL200 locks onto the reference signal 154. In this situation, thecontroller module 214 selects the fine calibration when thecommunications device is transitioning from the receive mode ofoperation to the transmit mode of operation.

As another example, also shown in FIG. 3, the communications device maybe operating in the TD-SCDMA standard. When the communications devicetransitions from the transmit mode of operation to the receive mode ofoperation, the TD-SCDMA standard allows 12.5 microseconds for thecontroller module 214 to calibrate the VCO 208 so that the reference PLL200 locks onto the reference signal 154. In this situation, thecontroller module 214 selects the offset calibration when thecommunications device is transitioning from the transmit mode ofoperation to the receive mode of operation because the LTE TDD standardprovides sufficient time to complete the offset calibration but notsufficient time to complete the fine calibration.

The controller module 214 performs the offset calibration by adjustingthe target signal 156 by the predetermined amount that relates to ashifting of the target signal 156 that results from transitioningbetween modes of operation. Typically, the predetermined amountrepresents a predetermined voltage and/or current that is coupled ontothe tuning signal 254 and/or shifting of the VCO tuning elements. Thispredetermined voltage, current, and/or VCO tuning elements shift thetarget signal 156 to accommodate for the difference that results fromtransitioning between modes of operation. After adjusting the targetsignal 156 by the predetermined amount, the reference PLL 200 settles tothe locked condition within the duration of time specified by thecommunications standards.

The fine calibration includes the offset calibration, as discussedabove, as well as another adjustment of the target frequency 156 tocompensate for operational conditions, such as temperature and/or powersupply to provide an example, of the communications device. Thecontroller module 214 adjusts the target signal 156 by the predeterminedamount in a substantially similar manner as the offset calibration. Thecontroller module 214 additionally adjusts the target signal 156 tocompensate for the operational conditions. Typically, this operationaladjustment may be characterized as being similar to the fullcalibration, but scaled down. The controller module 214 provides apredetermined number of different values for the frequency controlsignal 268 to cause the VCO 208 to provide the target signal 156 atdifferent frequencies. In an exemplary embodiment, the predeterminednumber of different values represents two different combinations of thesearching algorithm. However, this example is not limiting, thoseskilled in the relevant art(s) will recognize that the predeterminednumber of different values may represent any suitable number ofdifferent combinations of the searching algorithm so long as the finecalibration is completed within the time allotted by the communicationsstandard without departing from the spirit and scope of the presentdisclosure.

An Exemplary Calibration Requirement Table for Different CommunicationsStandards

FIG. 3 is a table that represents each type of calibration that may beused by the communications device for different communications standardsaccording to an exemplary embodiment of the present disclosure. FIG. 3includes exemplary communications standards in which a communicationsdevice, such as the communications device 100 to provide an example mayoperate in; however, those skilled in the relevant art(s) will recognizethat the communications device may operate in accordance with othercommunications standards without departing from the spirit and scope ofthe present disclosure.

For each communications standard, FIG. 3 depicts the time allowed byeach respective communications standard for a controller module, such asthe controller module 120 or the controller module 214 to provide someexamples, to calibrate a reference PLL, such as the reference PLL 108 orthe reference PLL 200 to provide some examples. For example, FIG. 3depicts that the TD-SCDMA communications standard allows 200microseconds for the controller module to properly calibrate thereference PLL when the communications device engages a communicationschannel. The 200 microseconds provided by the TD-SCDMA communicationsstandard may be sufficient to perform the full calibration. However, thecalibration period for the transition from the receive mode of operationto the transmit mode of operation provided by the TD-SCDMA is 75microseconds. The 75 microseconds may be sufficient to perform the finecalibration but not sufficient to perform the full calibration. Further,the calibration period for the transition from the transmit mode ofoperation to the receive mode of operation provided by the TD-SCDMA is12.5 microseconds. The 12.5 microseconds may be sufficient to performthe offset calibration but not sufficient to perform the fullcalibration and/or the fine calibration.

An Exemplary Voltage Controlled Oscillator (VCO)

FIG. 4 Illustrates a Block Diagram of an Exemplary Voltage Controlledoscillator (VCO) that may be used in the communications device accordingto an exemplary embodiment of the present disclosure. A controllermodule, such as the controller module 120 or the controller module 214to provide some examples, calibrates a VCO 400 in one of the fullcalibration, the fine calibration, and/or the offset calibration toprovide target outputs 452.1 and 452.2. The target outputs 452.1 and452.2 represent an exemplary embodiment of the target output 156. TheVCO 400 includes a fine frequency component 402 and a course frequencycomponent 404 which operate in conjunction with each other to providethe target signal 156.

The fine frequency component 402 includes a first fine capacitor 406.1,a second fine capacitor 406.2, and a varactor diode 408. As shown inFIG. 4, the tuning signal 254 is applied to the varactor diode 408. Thevaractor diode 408 represents a variable capacitance whose capacitanceis a function of the tuning signal 254. The first fine capacitor 406.1and the second fine capacitor 406.2 are coupled to the varactor diode408 to isolate the tuning signal 254 from the course frequency component404. Typically, the first fine capacitor 406.1 and the second finecapacitor 406.2 represent large capacitors when compared to the varactordiode 408 such that a capacitance of the fine frequency component 402 isdominated by the varactor diode 408.

The coarse frequency component 404 includes transistor switches 410.1through 410.n, first capacitors 412.1 through 412.n, second capacitors414.1 through 414.n, a first inductor 416.1 and a second inductor 416.2.The switches 410.1 through 410.n cause their corresponding firstcapacitors 412.1 through 412.n and second capacitors 414.1 through 414.nto contribute to a capacitance of the coarse frequency component 404when activated by a corresponding frequency control signal 450.1 through450.n. The frequency control signals 450.1 through 450.n represent anexemplary embodiment of the frequency control signal 268. In otherwords, the first capacitors 412.1 through 412.n and second capacitors414.1 through 414.n are switched in and out of the coarse frequencycomponent 404 by their corresponding switches 410.1 through 410.n. In anexemplary embodiment, the coarse frequency component 404 may includefirst capacitors 412.1 through 412.8 and second capacitors 414.1 through414.8. Those capacitors that are switched in the course frequencycomponent 404 contribute to the capacitance of the course frequencycomponent 404 while those capacitors that are switched out of the coursefrequency component 404 do not. The first inductor 416.1, the secondinductor 416.2, and the first capacitors 412.1 through 412.n and thesecond capacitors 414.1 through 414.n that are switched in the coursefrequency component 404 are configured and arranged to form a resonantcircuit.

The VCO 400 may include an oscillator core formed by the transistors418.1 and 418.2, and a biasing current source 420.

The controller module provides various frequency control signal 450.1through 450.n to switch various first capacitors 412.1 through 412.n andvarious second capacitors 414.1 through 414.n in and out of the coarsefrequency component 404 during the full calibration. The variousfrequency control signals 450.1 through 450.n are determined inaccordance with the searching algorithm. The switching in and out of thefirst capacitors 412.1 through 412.n and the second capacitors 414.1through 414.n in this manner adjusts a frequency of the target outputs452.1 and 452.2. Typically, the frequency of the target outputs 452.1and 452.2 is inversely related to the capacitance of the coarsefrequency component 404. The controller module continuously switches thefirst capacitors 412.1 through 412.n and the second capacitors 414.1through 414.n in accordance with the searching algorithm until thetarget outputs 452.1 and 452.2 are sufficiently related to the referencesignal 154 to allow the VCO 400 to lock onto the reference signal 154 byfinely adjusting the capacitance of the fine frequency component 402using the tuning signal 254.

The controller module adjusts the capacitance of the fine frequencycomponent 402 and/or adjusts frequency control signals 450.1 through450.n by the predetermined amount during the offset calibration.

The controller module adjusts the capacitance of the fine frequencycomponent 402 by the predetermined amount and adjusts the frequencycontrol signals 450.1 through 450.n by enabling a scaled down version ofthe full calibration cycle to adjust the capacitance of the coarsefrequency component 404 during the fine calibration.

An Exemplary Operational Control Flow of the Communication Device

FIG. 5 is a flowchart of exemplary operational steps of thecommunications device according to an exemplary embodiment of thepresent disclosure. The present disclosure is not limited to thisoperational description. Rather, it will be apparent to persons skilledin the relevant art(s) from the teachings herein that other operationalcontrol flows are within the scope and spirit of the present disclosure.The following discussion describes the steps in FIG. 5.

At step 510, the operational control flow determines a communicationschannel from among a plurality of communications channels that is to beused by a communications device to transmit and/or receive acommunications signal.

At step 520, the operational control flow performs the full calibrationto calibrate the communications device for the communications channel.Specifically, the operational control flow adjusts a reference PLL, suchas the reference PLL 108 or the reference PLL 200 to provide someexamples, within the communications device to lock onto a referencesignal, such as reference signal 154 to provide an example.

At step 530, the operational control flow receives the communicationssignal from step 510 from the communications channel from step 510and/or transmits the communications signal from step 510 onto thecommunications channel from step 510.

At step 540, the operational control flows determines whether thecommunications device is to select another communications channel fromamong the plurality of communications channels or to transition from thereceive mode of operation to the transmit mode of operation or from thetransmit mode of operation to the receive mode of operation. Forexample, the operational control flow determines whether thecommunications device is to subsequently transmit another communicationsonto the communications channel from step 510 after receiving thecommunications signal from step 510 from the communications channel fromstep 510. As another example, the operational control flow determineswhether the communications device is to subsequently receive anothercommunications from the communications channel from step 510 aftertransmit the communications signal from step 510 onto the communicationschannel from step 510.

The operational control flow proceeds to step 550 to transition betweenthese modes of operation or reverts back to step 510 to select anothercommunications channel.

At step 540, the operational control flow determines whether thecommunications device is to transition between the modes of operation ofstep 530. If so, the operational control flow proceeds to step 550,otherwise, the operational control reverts to step 510 to determineanother communications signal.

At step 550, the operational control flow determines the operationtransition time allowed by a communications standard. For example, theoperational control flow transitions from the transmit mode of operationto the receive mode of operation while operating in the TD-SCDMAcommunications standard. In this example, the operational control flowdetermines the transition time allowed by the TD-SCDMA communicationsstandard to transition from the transmit mode of operation to thereceive mode of operation which is approximately 12.5 microseconds.

At step 560, the operational control flow determines whether thecommunications standard provides sufficient time to calibrate thecommunications device using the fine calibration. If so, the operationalcontrol flow proceeds to step 570. Otherwise, the operational controlflow proceeds to step 580.

At step 570, the operational control flow performs the fine calibrationthen reverts to step 540.

At step 580, the operational control flow performs the offsetcalibration then reverts to step 540.

CONCLUSION

It is to be appreciated that the Detailed Description section, and notthe Abstract section, is intended to be used to interpret the claims.The Abstract section may set forth one or more, but not all exemplaryembodiments, of the present disclosure, and thus, are not intended tolimit the present disclosure and the appended claims in any way.

The present disclosure has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries may be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

It will be apparent to those skilled in the relevant art(s) that variouschanges in form and detail can be made therein without departing fromthe spirit and scope of the present disclosure. Thus the presentdisclosure should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A communications device, comprising: a reference phase-locked loop (PLL) configured to provide a target signal; and a controller configured to calibrate the reference PLL such that the target signal tracks a reference signal when the communications device transitions from a first mode of operation to a second mode of operation, wherein the controller is further configured to calibrate the reference PLL by adjusting the target frequency by a predetermined amount, the predetermined amount representing a pre-known shifting of a tuning signal that results from transitioning between the first mode of operation and the second mode of operation.
 2. The communications device of claim 1, wherein the first mode of operation is a receive mode of operation and the second mode of operation is a transmit mode of operation.
 3. The communications device of claim 1, wherein the first mode of operation is a transmit mode of operation and the second mode of operation is a receive mode of operation.
 4. The communications device of claim 1, wherein the reference PLL comprises: a voltage controlled oscillator (VCO) configured to provide the target signal in response to a tuning signal, wherein the controller module is configured to couple the predetermined amount onto the tuning signal to adjust the target signal.
 5. The communications device of claim 1, wherein the controller is further configured to further calibrate the reference PLL by further adjusting the target frequency to compensate for operational conditions.
 6. The communications device of claim 5, wherein the reference PLL comprises: a voltage controlled oscillator (VCO) configured to provide the target signal in response to the tuning signal and a frequency control signal, wherein the controller module is configured to couple the predetermined amount onto the tuning signal and adjust the frequency control signal by an amount based upon the operational conditions to adjust the target signal.
 7. The communications device of claim 1, wherein the communications device is configured to operate in accordance with a communications standard.
 8. The communications device of claim 7, wherein the controller is further configured to calibrate the reference PLL in a time allotted by the communications standard to transition from the first mode of operation to the second mode of operation.
 9. The communications device of claim 7, wherein the communications standard is selected from a group consisting of: Second-Generation Wireless Telephone Technology (2G); Third-Generation Wireless Telephone Technology (3G); Long Term Evolution Frequency-Division Duplexing (LTE FDD); Long Term Evolution Time-Division Duplexing (LTE TDD); and Time Division Synchronous Code Division Multiple Access (TD-SCDMA).
 10. The communications device of claim 1, wherein the controller module is configured to calibrate the reference PLL using a searching algorithm when the communications device engages a communications channel.
 11. A method for calibrating a reference phase-locked loop (PLL) when a communications device transitions from a first mode of operation to a second mode of operation, comprising: (a) providing a tuning signal; and (b) adjusting the tuning signal until a target signal tracks a reference signal, the adjusting including: adjusting the target frequency by a predetermined amount, the predetermined amount representing a pre-known shifting of the tuning signal that results from transitioning between the first mode of operation and the second mode of operation.
 12. The method of claim 11, wherein the first mode of operation is a receive mode of operation and the second mode of operation is a transmit mode of operation.
 13. The method of claim 11, wherein the first mode of operation is a transmit mode of operation and the second mode of operation is a receive mode of operation.
 14. The method of claim 11, wherein step (b) comprises: (b)(i) coupling the predetermined amount onto a tuning signal of a voltage controlled oscillator (VCO) to adjust the tuning signal.
 15. The method of claim 11, wherein the adjusting further comprises: adjusting the target frequency to compensate for operational conditions.
 16. The method of claim 15, wherein step (b) comprises: (b)(i) coupling the predetermined amount onto a tuning signal of a voltage controlled oscillator (VCO) to adjust the target signal; and (b)(ii) adjust a frequency control signal of a voltage controlled oscillator (VCO) by a scaled down version of a searching algorithm based upon a change in the operational conditions to adjust the target signal.
 17. The method of claim 11, wherein the communications device is configured to operate in accordance with a communications standard.
 18. The method of claim 17, wherein step (b) comprises: (b)(i) adjusting the tuning signal until the target signal tracks the reference signal in a time allotted by the communications standard to transition from the first mode of operation to the second mode of operation.
 19. The method of claim 17, wherein the communications standard is selected from a group consisting of: Second-Generation Wireless Telephone Technology (2G); Third-Generation Wireless Telephone Technology (3G); Long Term Evolution Frequency-Division Duplexing (LTE FDD); Long Term Evolution Time-Division Duplexing (LTE TDD); and Time Division Synchronous Code Division Multiple Access (TD-SCDMA).
 20. The method of claim 11, further comprising: (c) adjusting the tuning signal until the target signal tracks a reference signal using the searching algorithm when the communications device engages a communications channel. 